1. Field of the Invention
The present invention relates to a device for the detection of radiation that is dangerous to living beings, notably to human beings, and has effects that accumulate over time.
It is known that the gamma radiation produced in nuclear power stations is particularly dangerous. There are standards that lay down that the quantity of radiation received by any individual during his lifetime should stay below a determined quantity, expressed in millirems.
In the same way, radiologists and people who handle X-ray equipment are exposed to doses of radiation whose cumulative effect may be dangerous. Here again, standards lay down that the dose received by any individual in the course of his lifetime should not exceed a preset limit.
There are other types of radiation, such as ultraviolet radiation or radiation from charged particles, the accumulation of doses of exposure to these types of radiation in a given period may also be dangerous.
There are established procedures for checking the doses of radiation received by persons liable to be exposed to gamma radiation. In these procedures, the individuals concerned are made to carry devices that record the doses received.
2. Description of the Prior Art
Up till now, there have been two types of such devices: the first type of device is a photographic film carried by each individual liable to receive dangerous radiation. The drawback of such a device is that it does not give its bearer immediate information, and that this type of detection calls for a relatively complicated system of management of the information on the doses received. Besides, the film gives an indication only on the cumulative dose received during a determined period, generally of the order of one month, and the information that is then given to the bearer is generally very brief, all that he or she knows is whether the received dose is above or below the permissible threshold.
The second type of device takes the form of a bulky pack that houses the following elements: a radiation detector, circuits to memorize the cumulative dose, an alarm that gets triggered when the the dose rate goes beyond a permissible limit, a display of the doses accumulated while the instrument is carried, and means for connection with external circuits.
The devices of the second type are assigned on a general basis to the installation in which dangerous radiation may occur. They are usually placed in a rack where their batteries can be charged. To enter the installation, an individual has to use an identification badge that gives him access to the rack holding the devices and, at this instant, in the rack, a signal tells him which device is assigned to him. A centralized management system thus knows the relationship between the bearer and the device.
When the bearer leaves the installation, he returns the device to the rack and, at this instant, information on the cumulative doses is transmitted to a management center by means of the connector on the device.
This device is a bulky one, and dictates a system of management that is as cumbersome as in the case of the film. It lets the individual concerned know only the dose accumulated while he was wearing the device, i.e. during a period of some hours.
Furthermore, to measure the doses of radiation received by an individual, a portable device designed to record the radiation received by an individual over a lengthy period has been proposed (cf. patent application published as EP 0 300 054). However, the instrument described in this document is relatively bulky, and this fact may dissuade the user from wearing it constantly. In addition, the memorizing of data over a lengthy period is done in a removable permanent memory. This characteristic of being removable also is a factor of insecurity since, if the user forgets to insert the memory, the device in principle does not record the doses received.
The U.S. Pat. No. 4 608 655 describes a dosimeter of radiation received by persons working in the nuclear industry. This dosimeter takes the form of a constantly worn wristwatch. However, since this dosimeter is worn at the end of a member, it measures the doses received at this place and not in the entire body, notably in the trunk. Besides, the dosimeter described in this document carries out only a limited number of operations.
The present invention overcomes the above-mentioned drawbacks.